1. Field of the Invention
The present invention generally relates to a suspension system for a two-wheeled vehicle and, more particularly, to a vehicle employing bifurcated frame sections incorporating a resilient coupling therebetween.
2. Prior Art
The prior art discloses many designs for bicycles, light motorcycles and the like, all of which attempt to provide adjustable suspensions. Although it is understood the present invention is applicable to any type of two wheeled vehicle, for exemplary purposes the present invention shall be described with respect to a pedal driven bicycle.
The problems inherent in bicycle construction relate to the suspension or shock absorption capabilities as well as performance characteristics. A motor driven cycle taught by the prior art provides for a bifurcated frame having a fixed coupling intermediate the front and rear frames. To stabilize the suspension, a shock absorber is mounted intermediate the front and rear frames beneath the seat and a diagonal support of the rear frame. The problems inherent in this design relate to its inapplicability to a pedal driven bicycle. Since the front and rear frames are coupled at a fixed location, it fails to provide any means to deactivate the suspension.
A pedal driven bicycle must include means for deactivation of the suspension while pedaling yet permit activation on rough terrain when the user is not rotating the pedals. The present invention has solved this problem by providing for a selectively, adjustable coupling between the front and rear frames. By permitting the structural coupling between the front and rear frames to be pivotable, the orientation of a shock absorbing member relative to the axis of the crank and pedals will be optimized. Furthermore, by changing the axis of movement of the shock absorbing member, the force necessary to activate the suspension may be altered.
Another device taught by the prior art provides for front and rear frames which are pivotally connected directly adjacent the axis of rotation of the crank and pedal assembly. A horizontally disposed shock absorbing member is coupled between the front and rear frames forwardly of the seat support. As the front and rear frames pivotally change position relative to one another in response to the underlying terrain, the shock is absorbed by the resilient coupling of the shock absorber. This design exemplifies one of the problems inherent in bicycle construction. Where bicycles employ bifurcated frames as part of a system for absorbing shock, it is necessary to prevent the pedals from coming in contact the ground. This is generally referred to as "pedal droop." This problem may occur when the rotating crank and pedal assemblies are vertically deflected independent of the rear wheel.
In the device described by the prior art, the front frame and rear frame pivot about a point rearwardly of the crank assembly thereby allowing the crank and rotatable pedal assembly to vertically change position relative to the axis of the rear wheel. Pedal droop will occur if the vertical change of position of the crank and pedal assembly is excessive relative to the rear wheel. The present invention resolves the problem of pedal droop by utilizing a rear frame which stabilizes the position of the crank and pedal assembly relative to the rear wheel. Since the present invention utilizes a pivotal coupling intermediate the front and rear frames which is forwardly of the shock absorbing member, the problem of pedal droop is fully alleviated.
The present invention solves those problems left unresolved by the prior art by altering the manner in which the front and rear bicycle frames are coupled to one another. The bicycle is comprised of a bifurcated frame assembly. The front frame includes the front fork and wheel, handlebar and steering assembly and the seat. The seat is coupled to the steering assembly by a top tube, a diagonal support tube being extended forwardly and downwardly therefrom. A supporting plate secures the diagonal support tube to the steering assembly. The support plate provides an optimum pivot point to which the rear frame may be coupled. The rear frame is generally triangular and includes the crank and pedal assemblies, extending rear arms, coaxial rear and center stays and the rear wheel. The crank assembly is joined to the forward terminus of the center stay by a diagonal down tube. At the forward intersection between the center stay and diagonal down tube the rear frame is pivotally coupled to the support plates of the front frame. A shock absorbing member is mounted between the intersection of the center and rear stays of the rear frame and the diagonal support tube of the front frame. By adjusting the position at which the upper end of the shock absorber is secured to the diagonal support tube, the suspension may be adjusted to compensate for the force imposed on the bicycle seat (i.e., weight of the rider). By optimizing the position of the pivotal coupling intermediate the front and rear frames, the force necessary to activate the shock absorbing suspension may be set to improve performance characteristics.